1. Field of the Invention
This invention relates to pneumatic control valves for use with pneumatically driven motors. In particular, this invention relates to a pneumatic control valve for a windshield wiper motor utilizing the combined park valve, run valve and regulator valve assembly.
2. Description of the Prior Art
It can be appreciated that when a control valve and a pneumatically-driven motor such as in U.S. Pat. Nos. 2,678,029 issued to Sprague, et al. and 3,257,910 issued to Gates are first activated, the various moving elements of each, such as O-rings, etc., have increased static frictional forces associated therewith. In order to overcome the increased starting frictional forces, an increased amount of air pressure must be initially provided. In valves of the prior art, this increased air pressure is supplied by an operator manually setting a valve control cam to a higher pressure position. This produces an increased value of regulated air pressure sufficient to overcome the starting static frictional forces and to start the wiper motor. Once the wiper motor achieves a desired operating speed, the operator must manually reset the control cam to a normal operating position. It is desirable that an air-control valve for a windshield wiper motor include a means for automatically providing higher air pressure to overcome initial static frictional forces.
Parking of a wiper motor is not automatically provided by prior art control devices such as shown in U.S. Pat. Nos. 2,616,400 issued to Sprague, et al. and 3,005,455 issued to Riester, et al. Parking of a wiper motor occurs when air pressure is applied to a separate park port of the wiper motor while air pressure is simultaneously applied to the run port of the wiper motor. The wiper motor operates until the wiper blades come to a park position, at which point the wiper motor is stopped. Prior art control devices require that an operator maintain the wiper control in a separate park position until the wipers are locked in the park position. A desirable feature for a wiper control is for the wiper control to provide means for automatically parking the wiper motor when the control is placed in an off position.
Prior art controls for wiper motors have combined a separate air regulator valve and a separate park control valve in one housing. The components and functions of these valves have been independent of each other. For example, one prior art control for a wiper motor has an air pressure regulator valve and a park control valve placed next to each other, but each valve is independently controlled by a separate push pin which rides on a separate cam surface of a rotatable operator control. In addition, this type of valve requires that an operator first manually position the control to the park position. After the wiper motor is parked, the operator is required to manually position the control to an off position. It is desirable that the components of a wiper control be integrally combined to produce a compact unit which automatically increases air pressure and which automatically parks a wiper motor. A similar control device and motor is shown in Gates U.S. Pat. No. 3,257,910.